Alloy bodies having improved magnetic properties and process for producing same



y 15, 1962 .1. L. WALTER ETAL 3,034,935

ALLOY BODIES HAVING IMPROVED MAGNETIC PROPERTIES AND PROCESS FOR PRODUCING SAME 2 Sheets-Sheet 1 Filed Dec. 1, 1958 Fig. 2

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May 15, 1962 J. WALTER ETAL 3, 3

ALLOY BODIES HAVING IMPROVED MAGNETIC PROPERTIES AND PROCESS FOR PRODUCING SAME 2 Sheets-Sheet 2 Filed Dec. 1, 1958 Field Sfrengf/r Oersfeds 3 9 H u 000 0 0 nw mu 4 .9 H 6 r 0 000 womooao mm mJ/J Annealed W/fh Magnetic Field myemorg P ///r 1/; R//' 0' I" am e o e a my 0'00 10!] J h L Wq/fef' Howard C. F/ed/er,

by T heir Afforney- United States Patent M 3,034,935 ALLOY BGDIES HAVING IMPROVED MAGNETIC IROPERTIES AND PROCESS FOR PRODUCING AME John L. Walter, Scotia, and Howard C. Fiedler, Schenectady, N.Y., assignors to General Electric Company, a corporation of New York Filed Dec. 1, 1958, Ser. No. 777,394 Claims. (Cl. 148-31.55)

This invention relates to bodies composed of magnetic alloys and more particularly to sheet-like bodies composed principally of iron and having improved magnetic and magnetostrictive properties and to a method for producing the improved properties in the sheet-like bodies.

Iron base alloys consisting of at least 92 percent iron and containing alloying agents such as silicon, aluminum, molybdenum, or some combination thereof, have found extensive use in electrical applications. For example, iron containing from 2 to 5 weight percent silicon, iron containing up to 8 weight percent aluminum, and iron containing up to 8 weight percent of combinations of silicon and aluminum have been widely used as transformer core materials.

The electrical and magnetic properties of the present alloys have been improved by aligning the unit cubes so that one or more easiest directions of magnetization exist. This invention is specifically concerned with sheet-like bodies composed of iron-base alloys having a body-centered cubic crystal structure in which a majority of the constituent grains are aligned in the (100) [001] orientation to produce two easiest directions of magnetization in the plane of the sheet. This orientation is generally referred to as cube texture and is typified by having a majority of the unit cubes so oriented that two cube faces are generally parallel to the rolling surface of the sheetlike body, two other faces are perpendicular to the rolling surface and generally parallel to the rolling direction and the remaining two unit cube faces are perpendicular to the rolling direction and to the rolling surface. A more complete discussion of the cube texture grain orientation and of a method for producing the orientation in a sheetlike body is found in the copending application Serial No. 610,909 of Hibbard et al., filed September 20 1956, and assigned to the same assignee as the present invention.

It is therefore a principal object of this invention to provide sheet-like bodies composed principally of ironposed of iron-base body-centered cubic alloys.

Other objects and advantages will be in part obvious and in part explained by reference to the accompanying specification and drawings.

FIG. 1 shows the distribution of the magnetic domains within a silicon-iron body having cube texture;

FIG. 2 shows the distribution of the magnetic domains of thesilicon-iron body of FIG. 1 following magnetic annealing;

FIG. 3 is a hysteresis loop illustrating the magnetic properties of a cube texture silicon-iron body annealed 3,034,935 Patented May 15, 1962 2 without a magnetic field and measured parallel to the rolling direction; and

FIG. 4 is a hysteresis loop of a cube texture siliconiron body annealed in a magnetic field parallel to the rolling direction and measured parallel to the rolling direction.

Generally, this invention concerns sheet-like bodies composed of iron-base body-centered cubic alloys having cube texture orientation, which alloys have improved magnetic properties including lower magnetostrictive characteristics, and to a method for producing such bodies.

More specifically, the alloys used are iron-base alloys containing 2 to 5 percent silicon, up to 8 percent aluminum, up to 8 percent molybdenum and iron base alloys containing some combination of the three listed alloying additives. Other materials, such as carbon, oxygen and nitrogen are normally present in trace percentages, normally less than 0.02 percent, 0.006 percent and 0.001 percent, respectively. These alloys are suitably rolled into sheet-like bodies having the [001] orientation so that two easiest directions of magnetization are in the plane, or rolling surface of the body. Bodies having at least 65 percent of the constituent grains oriented in the (100) [001] crystalline orientation are preferred, although lower percentage orientations can be used in some instances.

Generally, the improved magnetic properties are obtained by taking appropriately sized sheet-like bodies of the general compositions previously mentioned and heating them to an elevated temperature while subjecting them to a magnetic field of predetermined magnitude and direction. The bodies are then cooled from the elevated temperature at a rate of about 100 an hour in a dry hydrogen atmosphere while the magnetic field is maintained. The magnetic field causes an orientation or ordering of the magnetic domains within the material, which alignment is generally parallel to the direction in which the magnetic flux is directed. The magnetic field can be made to either align the magnetic domains parallel the longitudinal or rolling direction of the metal body or can be directed at right angles thereto. Approximately the same results are obtained from the magnetic and magnetostrictive standpoints, due to the fact that the cube texture orientation provides two easiest directions of magnetization. The magnetostrictive values fall within the range of from about 0.5 to 1.0 microinch per inch and preferably within the range of from about 0.1 to 1.0 microinch per inch.

Referring to FIGS. 1 and 2 of the drawings, the effect on the magnetic domains of annealing in a magnetic field can be seen quite clearly. Referring to FIG. 1 first, lines 10 indicate the boundaries of magnetic domains and it is apparent that the lines exhibit no substantial degree of common alignment. Since the boundaries are not aligned it follows that the magnetic domains are similarly non-aligned and that optimum magnetic properties can not be obtained.

Since the only dilference between the body ofFIG. 1 and FIG. 2 is the fact that the body is magnetically annealed in FIG. 2, the effect of the magnetic anneal is evident. In FIG. 2 the lines 10 are generally parallel the rolling direction, this being the direction in which the magnetic field was directed.

To illustrate the effect of magnetic annealing on the magnetic properties of the bodies, reference is made to FIGS. 3 and 4. Specifically, the loop 15 of FIG. 3 shows the characteristics of the material when it is annealed without being subjected to a magnetic field. The residual magnetism (Br) is relatively low and the entire curve is somewhat sheared so that while the material can be used in electrical applications such as transformers, it does not represent a material having optimum characteristics. On the other hand, the hysteresis loop 16 of FIG. 4 is markedly different in that it has been squared so that the residual magnetism (Br) is at a maximum.

Material having the properties indicated by loop 16 would be more useful in transformer applications than one having the properties evidenced by loop 15. The difference in the properties of the materials was brought about by magnetically annealing the material to align the majority of the magnetic domains in generally the same direction, the direction in the present instance being parallel to the rolling direction of the sheet-like body.

Results obtained from magnetic annealing with alignment of the domains are illustrated by the following. A body of cube texture silicon-iron was prepared and tested and annealed, first without a magnetic field, and subsequently in the presence of an applied magnetic field to align the magnetic domains. The watt losses, in watts per pound, and magnetostriction, in microinches per inch of the sample before and after magnetic annealing were then measured parallel to the rolling direction with the body subjected to a field of about 15,000 gauss. The body annealed Without the magnetic field has a Watt loss of .67 watt per pound and a magnetostriction of 3.9 microinches per inch, whereas the magnetically annealed body had a watt loss of .58 watt per pound and magnetostriction of only .4 microinch per inch.

As a further example illustrating the effect of the mag netic anneal, an iron-base alloy having about 3 percent silicon and other incidental impurities such as oxygen, nitrogen and carbon, and having a majority of the constituent grains oriented in the (100) [001] direction was heated to about 800 C. at a rate of about 100 per hour. The body Was held at this temperature for about one hour and simultaneously subjected to a magnetic field of about 50 oersteds, the field being applied parallel to the rolling direction. Following annealing, the body remained subjected to the magnetic field and cooled at the rate of 100 C. an hour in dry hydrogen. The maximum permeability increased an average of 13 percent and the residual reduction (Br) increased by 11 percent.

Additional sample bodies, about 12 mils thick and containing about 3 percent silicon, balance substantially all iron, were cut in the cross grain direction and annealed in the manner just described, with the exception that the magnetic field was directed at right angles to the rolling direction. Average increases of 27 percent and 29 percent in residual induction and maximum permeability, respectively, were obtained when measured at right angles to the rolling direction, i.e., in the direction of the field. The test results are fully set forth in Table I.

Table 1 Before Magnetic Anneal After Magnetic Anneal 0. 14 0. 11 oersteds. 7,100 11, 600 gauss. 15, 200 15, 400 gauss.

4 Table II Before Magnetic Anueal After Magnetic Anneal .20 20 oersteds. 6, 7, 900 gauss. 11, 600 12,150 gauss. 14, 650 21,

Thus, from a review of the values set forth in Tables I and II, it is apparent that the magnetic annealing procedure results in material improvement in the magnetic properties of the bodies in both the longitudinal, and cross directions. Of course, the improvements in a given body occur only in the direction in which the field is applied, a slight decrease in magnetic properties occurring in the other direction.

The magnetostriction of sheet-like bodies of suitable composition for use as core materials is, as already mentioned, an important factor to be considered. Magnetostriction is a change in the physical dimensions of a piece of metal resulting from passage of magnetic energy therethrough. In the case of core parts subjected to magnetic fields, this change in dimensions results in vibration causing objectionable noise or hum. The vibration may also cause unnecessary Wear decreasing transformer performance and usable life. It is particularly important in a cube-textured alloy, since the magnetostriction may be quite high in the rolling direction. One of the important features of this invention is the provision of a cube-textured iron-base alloy having low magnetostriction.

To illustrate the effect of magnetic annealing, two samples were prepared from 12 mil sheet material composed essentially of 3 percent silicon and the balance substantially all iron. These bodies were measured prior to and following a magnetic anneal. The magnetic field is parallel to the rolling directionso that the magnetic domains would align in the same direction. The samples were measured in a magnetic field of 15.5 kilogausses and the magnetostriction measured. The results are shown in Table III.

Table III Magnetostrietlon Sample (microdnches/ inch) 1 (annealed) 5.0 2 (annealed) 3.9 1 (mag. annealed) 0. 5 2 (mag. annealed) 0. 4

Thus, the present invention provides bodies of cube textured iron-base alloys which have improved magnetostriction characteristics, as Well as improved magnetic properties. Also, a method for achieving these improved characteristics is provided.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A rolled, sheet-like body of a body-centered cubic magnetic material consisting essentially of at least 92 percent iron, up to 5 percent silicon, up to 5 percent molybdenum, and up to 8 percent aluminum, and having a majority of constituent grains thereof in the (100') [001] orientation to provide two directions of easiest magnetization in the plane of said sheet-like body, one of said directions being parallel to the rolling direction and the other said direction substantially transverse thereto, said body further having a majority of the magnetic domains aligned generally parallel one of said easiest directions of magnetizations and having a magnetostriction of from about 0.5 to 1.0 when subjected to a magnetic field of about 15.5 kilogausses applied generally parallel to the direction of the domain alignment.

2. A sheet-like body as defined in claim 1 wherein said magnetostriction ranges from about -O.1 to about 0.5

microinch per inch in a magnetic field of about 15.5 kilogausses.

3. A rolled, sheet-like body as defined in claim 1 Wherein said magnetic material consists essentially of at least 92 percent iron, up to 5 percent silicon, and up to 8 percent aluminum.

4. A rolled, sheet-like body of a body-centered cubic material consisting essentially of from about 2 to about 5 percent silicon, balance substantially all iron, and having a majority of constituent grains thereof in the (100) [001] orientation to provide two directions of easiest magnetization in the plane of said sheet-like body, one of said directions being parallel to the rolling direction and the other said direction substantially transverse thereto, said body further having a majority of the magnetic domains aligned generally parallel one of said easiest directions of magnetization and having a magnetostriction of from about 0.5 to 1.0 when subjected to a magnetic field of about 15.5 kilogausses applied generally parallel to the direction of the domain alignment.

5. A rolled, sheet-like body as defined in claim 4 wherein at least 65 percent of the constituent grains thereof are oriented in the 100) [001] direction.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Bozorth: Ferromagnetism, 1951, D. Van Nostrand 00., Inc., page 680. Library call number QC753 B69. Metal Progress, Heat Treatment in a Magnetic Field,

20 January 1952, pages 106 and 107. 

1. A ROLLED, SHEET-LIKE BODY OF A BODY-CENTERED CUBIC MAGNETIC MATERIAL CONSISTING ESSENTIALLY OF AT LEAST 92 PERCENT IRON, UP TO 5 PERCENT SILICON, UP TO 5 PERCENT MOLYBDENUM, AND UP TO 8 PERCENT ALUMINUM, AND HAVING A MAJORITY OF CONSTITUENT GRAINS THEREOF IN THE (100) (001) ORIENTATION TO PROVIDE TWO DIRECTIONS OF EASIEST MAGNETIZATION IN THE PLANE OF SAID SHEET-LIKE BODY, ONE OF SAID DIRECTIONS BEING PARALLEL TO THE ROLLING DIRECTION AND THE OTHER SAID DIRECTION SUBSTANTIALLY TRANSVERSE THERETO, SAID BODY FURTHER HAVING A MAJORITY OF THE MAGNETIC DOMAINS ALIGNED GENERALLY PARALLEL ONE OF SAID EASIEST DIRECTIONS OF MAGNETIZATIONS AND HAVING A MAGNETOSTRICTION OF FROM ABOUT -0.5 TO 1.0 WHEN SUBJECTED TO A MAGNETIC FIELD OF ABOUT 15.5 KILOGAUSSES APPLIED GENERALLY PARALLEL TO THE DIRECTION OF THE DOMAIN ALIGNMENT. 